Research and development in telecommunications applications have been expanding to meet the increasing popularity in the Internet. One particular application relates to digital subscriber line (DSL) technologies, including symmetric DSL (SDSL) and asymmetric DSL (ADSL) and high data rate DSL (HDSL), to name a few. DSL can employ a variety of possible information rates and protocols depending on the type of DSL being implemented. DSL is a modem technology that converts existing telephone lines into access paths for multimedia and high speed data communications. DSL utilizes advanced digital signal processing and creative algorithms to provide greater amounts of information through twisted-pair telephone lines. One particular type of DSL system relates to multi-pair DSL systems employing a plurality of twisted-pair telephone lines in a bundle, which is often referred to as a vectored system.
Digital Subscriber Line (DSL) transmission can be constrained by interference from one or more sources when a signal from one copper pair inductively couples with the signal in another pair. This type of interference, which can distort the received signal from the originally intended signal, is commonly referred to as crosstalk interference. Cross-talk interference can originate from two kinds of sources. For example, crosstalk may originate from a transmitter belonging to the vectored system, which is referred to as in-domain cross talk. Crosstalk interference may also originate from a transmitter outside the vectored system, which is referred to as alien or out-of-domain crosstalk. The potential for crosstalk exists most predominantly at the ends of the loops where numerous pairs come together to be connected to the local exchange carriers' (LECs') active central office (CO) equipment or the customer's termination equipment. These sources may give rise to either of Far-End-Crosstalk (FEXT) and Near-End-Crosstalk (NEXT). Regardless of the type of crosstalk or its source, crosstalk operates to reduce signal-to-noise ratios on a given line.
As DSL technology advances and processing power increases, there is continuing interest in techniques for reducing crosstalk interference.